The expression "New Synthetic Stimulants" include classes of psychoactive compounds that share subjective effects in humans such as boosted mood or euphoria, feelings of empathy or compassion, increased sociability and sex drive, perceived increased ability to learn and focus, increased energy and alertness, with unpleasant outcomes like increased blood pressure and heart rate, paranoia or aberrations, decreased appetite, raised body temperature, clenched jaw or grinding teeth, dry mouth, insomnia, hallucinations, and aggressive or violent behavior. Synthetic stimulants act in the brain by increasing concentrations of neurotransmitters, mainly dopamine and serotonin. Dopamine is involved in attention, reward, and motivation whereas serotonin is involved in generating feelings of happiness and pleasure. Synthetic stimulants act on the two brain systems to different extents, accounting for their range of effects. Noradrenaline release is also stimulated by these compounds, but to a minor degree. In any case, long-term use of synthetic stimulants exhausts dopamine and serotonin systems in the brain. The nerve cells become desensitized to the drugs, which makes them resistant to the brain's own signaling molecules. This leads to tolerance and dependence, which can easily turn into addiction. Like classic stimulants (e.g., cocaine, methamphetamine), new synthetic stimulants can be highly addictive.